The present invention relates to a hollow fiber membrane air 5 drier in which air is dehumidified. A known hollow fiber membrane air drier comprises hollow fiber membranes made of polymer fibers which allow water vapor to pass easily through the membranes through the hollow fiber membranes, but makes a gas difficult to pass, the membrane being included in a casing, humidified compressed air being supplied in the hollow fiber membrane to make vapor penetrated out so that dehumidified or dried air may be obtained.
The hollow fiber membrane air drier has no movable parts and need not electric energy; has small size and light-weight; provides high durability and generates no drainage. Such an air drier is very advantageous and widely used in a lot of equipment.
To carry out dehumidification continuously in such a hollow fiber membrane air drier, it is necessary for the outside of the hollow fiber membrane to be kept in lower water vapor partial pressure.
Pressure of dried air is partially reduced and relative humidity is reduced, so that it is forwarded to the outside of the hollow fiber membrane to cause difference in pressure of water vapor. It is discharged to air with water vapor which passes through the hollow fiber membrane, which is called as a water-vapor purging dehumidifier which is generally used.
However, without allowing purging air to flow, an evacuating dehumidifier is suggested in which the outside of a hollow fiber membrane is evacuated to vacuum and reduced in water vapor partial pressure for dehumidification. However, energy for vacuum source is required.
In a hollow fiber membrane air drier, to prevent dehumidified partial air from being used for purging, without generating purging air as above, the outside of the hollow fiber membrane is evacuated by a vacuum source. If abnormality should occur in the vacuum source to cause failure in evacuation, the hollow fiber membrane air drier will lose its function. So air that is not dehumidified is forwarded to the end of use to result in inconvenience in quality of products and during operation.
In a water-vapor purging dehumidifier in which dehumidified air is partially used, if its part should be out of order so that dried air is not partially forwarded to the outside of the hollow fiber membrane, similar disadvantages will occur.
If a dehumidifier involves abnormality to cause lack in performance, no means for going on dehumidification without inconvenience exist so far as the inventor knows.